Unwrap the Uncrustables and spray both sides with cooking spray or lightly spread butter. This is optional but will give them a terrific golden color and crisp texture.
Cook
Place them inside the air fryer with the cooking tray in place. Set the temperature to 375F and cook frozen Uncrustables for 7 to 8 minutes. If they're thawed, they only need 5 minutes to cook. Flipping them over halfway through is optional but ensures even color.
Serve
Transfer to a plate or board and let it cool for 1 to 2 minutes before eating; the filling will be hot.
Notes
Air fryers vary, so check the sandwich toward the end of the cooking time.